In order to protect a building from rainwater or moisture in the air, a construction method has been conventionally employed in which a waterproof sheet is attached to the external wall base or openings such as windows and doors.
A common sheet is both waterproof and moisture-proof, and thus cannot release water accumulated on the sheet at the base side to the outside through the waterproof sheet. For this reason, there are problems such as that the wood or the steel frame is corroded to deteriorate the building, and that mold grows so that the indoor air is contaminated and the health of the resident is then disturbed.
In order to solve such problems, a waterproof sheet having both waterproofness and moisture permeability has been developed. Typical examples of such a moisture-permeable waterproof sheet include nonwoven fabric formed by flashspinning. Nonwoven fabric formed by flashspinning is disclosed for example in Patent Document 1, and the production method thereof is disclosed for example in Patent Document 2. Nonwoven fabric obtained thereby has a moderate aperture, and blocks water but lets air and water vapor pass therethrough. As such nonwoven fabric, Tyvek (product of DuPont, registered trademark) produced by thermo-compression bonding three-dimensional plexifilamentary fibers of high-density polyethylene. This moisture-permeable waterproof sheet enables to prevent entry of water from the outside as well as to release the water accumulated inside to the outside as water vapor, thereby solving the above problems.
However, the locations around the openings such as windows/doors are not flat, and thus the waterproof sheet alone cannot easily form a waterproof layer. Therefore, such a location is usually sealed with the aid of an adhesive-backed waterproof tape. In this case, since the adhesive layer is formed from a rubber adhesive or asphalt adhesive, the moisture permeability of the entire tape decreases to raise the same problems as in common waterproof sheets.
Also in the case of the external wall base, since nails and adhesive tapes are used for the overlapping portion of moisture-permeable waterproof sheets, water sometimes enters the inside from gaps between the sheets and the nails or adhesive tapes during a long-term use.
Patent Document 3, for example, teaches a liquid waterproof coating material having moisture permeability to solve such a waterproofing problem in the locations around the openings and the external wall base. In this case, since a waterproof material layer is formed continuously, the gaps due to the adhesive-backed waterproof tapes or nails are significantly reduced. This enables energy saving owing to reduction in the internal air leakage, in addition to solving the problems such as the deterioration of the building and health disturbance.
However, the composition used for the liquid waterproof coating material as disclosed in Patent Document 3 contains a latex polymer (aqueous emulsion) which requires a long time for forming a coating film at low temperatures or high humidity. Disadvantageously, the composition has low workability in winter. Also, latex polymer coating films, not having high elasticity, cannot follow the distortion formed over a long period of time in the base, causing cracks, fractures, and the like therein to bring a problem such as a decrease in the waterproofness.
Meanwhile, organic polymers containing at least one reactive silyl group per molecule are known to be cross-linked by siloxane bond formation involving reactions such as hydrolysis of the reactive silyl group due to moisture or the like even at room temperature, and thereby provide rubbery cured products.
Among these reactive silyl group-containing organic polymers, those polymers which have a main chain skeleton of a polyoxyalkylene polymer are disclosed in Patent Document 4 and the like. These polymers have already been industrially produced and widely used in various applications such as sealants and adhesives.
Since reactive silyl group-containing polyoxyalkylene polymers have comparatively low viscosity, a nonaqueous liquid waterproof coating material having sufficient workability can be designed by using such a polymer even with no or small amount of a solvent. Further, reactive silyl group-containing polyoxyalkylene polymers can have practical curability even at low temperatures, and are thus workable in winter. Moreover, since such a reactive silyl group-containing polyoxyalkylene polymer is cured into a rubbery product having good elasticity, the cured polymer is expected to sufficiently follow the distortion of the base.
However, a liquid waterproof coating material containing a known curable composition containing the above polymer has the similar waterproofness to a waterproof sheet but does not have sufficient moisture permeability. For this reason, the above problems have not been completely solved. The present invention aims to increase the moisture permeability of the liquid waterproof coating material and maintain the moisture permeability for a long period of time while maintaining its waterproofness.
Patent Document 1: JP-B S42-19520 (U.S. Pat. No. 3,169,899)
Patent Document 2: JP-B S43-21112 (U.S. Pat. No. 3,532,589)
Patent Document 3: US 2007/0042196 A
Patent Document 4: JP-A 355-9669 (U.S. Pat. No. 4,507,469)